1. Field
The presently disclosed subject matter relates to a semiconductor optical device including LEDs, laser diodes, photodiodes, etc. and more particularly to a surface mount semiconductor optical device, which emits/detects light in parallel with a mounting surface thereof (e.g., a side view type semiconductor device).
2. Description of the Related Art
A surface mount semiconductor optical device having a semiconductor optical chip mounted in a casing that is provided with lead frame electrodes insert-formed by a resin includes the following two types. One is a top view type, in which a light ray axis is perpendicular to a circuit board on which the chip is mounted. The other is a side view type, in which a light ray axis is parallel to the circuit board.
A semiconductor optical device of the side view type is generally used as a light source for use with a light guide material in a flat panel display, which is used as a back light unit for a LCD panel, a panel lighting apparatus, general lighting and the like.
The structure shown in FIG. 16 is a typical structure for a conventional semiconductor optical device 52 of the side view type. The structure includes a casing 51 that is provided with lead frame electrodes 50(a), 50(c), 50(b), 50(d) insert-formed by a resin. The casing 51 includes a concave-shaped cavity with an opening and a bottom portion at which each end portion 50a, 50b of the lead frame electrodes that are respectively separated is exposed. Each other end portion 50c, 50d is bent forwards and backwards towards or parallel with an optical or light ray axis of the semiconductor optical device 52. The other end portions 50c, 50d extend outside the bottom surface at the same level as the bottom portion by extending from the bottom portion to an area outside of the casing 51.
An LED chip 53 is mounted on the exposed end portion 50a via a conductive material and is electrically connected at one electrode thereof to the exposed end portion 50a. The other electrode of the LED chip 53 is electrically connected to the exposed end portion 50b via a bonding wire 54. An encapsulating transparent resin is disposed in the concave-shaped cavity for encapsulating chips 53 and bonding wires 54. A semiconductor optical device such as a surface mount LED device of the side view type is described in further detail, for example, in Japanese Patent Application Laid Open JP2004-193537 and its English translation, which are hereby incorporated in their entirety by reference.
Because an LED chip used for the above-described conventional semiconductor optical device is made from semiconductor materials, the electrical and optical characteristics thereof are dependent on temperature. That is, when a current flows to an LED chip and the LED chip is lit, a light-emitting efficiency thereof decreases due to a self-fever condition caused by an LED current that flows into the LED chip and elevates the temperature of the MED chip.
Thus, in order to prevent the decrease of the light-emitting efficiency one can radiate the self-fever, which is generated during light-emitting of the LED chip. The self-fever generated in an LED chip may be generally radiated from an LED chip to an area outside of the semiconductor optical device through the lead frame electrodes that include an LED chip mounted thereon. The lead frame electrodes may greatly contribute to the prevention of the self-fever condition in an LED chip both directly and indirectly. Therefore, effective radiation characteristic design for the lead frame electrode is an important factor for preventing a rise of the self-fever during light-emitting of the LED chip.
When the above-described conventional semiconductor optical device 52 is considered, both the one lead frame electrode mounted an LED chip on the exposed one end portion thereof and the other lead frame electrode connected to the exposed end portion thereof via a bonding wire extend into the same surface of the concave-shaped cavity to and from the same outside surface.
In a surface mount semiconductor optical device that is miniaturized, the greater the amount of lead frame electrodes that lead from the casing to the outside, the narrower the width of each lead frame electrode is in order to maintain a miniaturization of the device size.
However, the narrower the width of the lead frame electrode, the smaller the cross-sectional area that is perpendicular to current flow direction in the LED becomes. As a result, a thermal conduction decrease of the lead frame electrode is caused by an increase of thermal resistance, and may result in a loss of radiation ability.
The lead frame electrode is generally formed by stamping out a sheet metal using a press die. Each interval in the sheet metal between respective adjacent lead frame electrodes should at least be wider than a thickness of the lead frame electrode by restriction of the pressing process. Thus, the increase in the number of lead frame electrodes results in a restrictive factor for designing a miniaturization of a semiconductor optical device size.
If the number of lead frame electrodes increases, each area at the other end portions of lead frame electrodes that leads from the casing should be small due to a layout restriction, e.g., for maintaining a predetermined interval between respective adjacent lead frame electrodes. When the semiconductor optical device is mounted on a circuit board, the function of the other end portions includes: fixing the device to the circuit board by mounting on conductor patterns of a circuit board; electrically connecting the device to a circuit board; and conducting the self-fever of LED chips to conductor patterns of a circuit board through the lead frame electrodes upon which LED chips are mounted.
If the area of respective other end portions of the lead frame electrodes becomes small, the contact area with conductor patterns of a circuit board becomes small. Thus, the decrease in area of respective other end portions may result in a decrease of mounting reliability because the semiconductor optical device may not be mounted with strength and confidence by the respective other end portions, and may result in a decrease of the light-emitting efficiency due to a rise of the operating temperature of an LED chip by weakening radiating efficiency of the LED chip's self-fever.
Furthermore, when a complex light-emitting color is emitted by a plurality of different light-emitting color LED chips, it is difficult to maintain a miniaturization of a semiconductor optical device size and to provide equal spacing intervals for the respective adjacent LED chips due to layout restrictions of the lead frame electrodes when positions of the one end portions must be moved in accordance with a layout of LED chips. If each interval of the respective adjacent LED chips is forced to be equal, a semiconductor optical device may become large and may result in a decrease in the color rendering index because of long intervals between respective adjacent LED chips.
The disclosed subject matter has been devised in consideration of the above and other problems and characteristics. The disclosed subject matter can include a semiconductor optical device, which includes a stable optical characteristic with an excellent radiant efficiency, a high mounting reliability, and a possibility for design miniaturization.